Note 6 - Share-based Compensation - Summary of Stock-Settled Stock Appreciation Rights Transactions (Details) - Stock Appreciation Rights (SARs) [Member] - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Outstanding SARS, shares (in shares)			325,506
Outstanding SARS, weighted average exercise price (in dollars per share)			$ 10.26
Granted, shares (in shares)			43,988	58,108
Granted, weighted average exercise price (in dollars per share)			$ 16.97
Exercised, shares (in shares)	(68,698)	(39,584)	(128,062)	(75,792)
Exercised, weighted average exercise price (in dollars per share)			$ 6.87
Outstanding SARS, shares (in shares)	241,432		241,432
Outstanding SARS, weighted average exercise price (in dollars per share)	$ 13.28		$ 13.28